Accounting for Share-Based Compensation 2 (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Dec. 31, 2012
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	$ 100
Weighted average period expected to be recognized	2 years 0 months 0 days
Stock Option Awards [Member]
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	4
Weighted average period expected to be recognized	2 years 1 month 6 days
Restricted Stock Units [Member]
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	16
Weighted average period expected to be recognized	2 years 0 months 0 days
Restricted Stock Awards [Member]
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	66
Weighted average period expected to be recognized	1 year 10 months 24 days
Performance Share Units [Member]
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	$ 14
Weighted average period expected to be recognized	2 years 9 months 18 days